I have a pattern for a washtowel. However I want to knit hand towel, so probably double that size. Would it be okay to just double the number of cast on stitches? And if so, how do I then handle/count the pattern stitches? Do I just double all the stitches in the pattern rows?
If there is a pattern stitch the best way to increase is to do a multiple of what’re that is. Take ribbing for example - a k2p2 rib is a multiple of 4. You need 4 stitches to complete one repeat. So you need to figure out how many stitches complete the repeat and increase accordingly.
That is not always possible of course if the pattern varies. you may need to just put a wider border. Since I don’t know what pattern it is I can’t say for sure. It may be possible to just double it.